1. Field of the Invention
The present invention relates to a power supply system, and more particularly, to a power supply system capable of both charging and discharging functions.
2. Description of the Prior Art
With developments of technology and advancements in the industry, mobile devices such as mobile phones, GPS navigator systems, tablets, laptops and wearable devices have become indispensable in our daily life. In order to facilitate a user to carry, the mobile devices are always equipped with batteries for power storage, which provides the power required during operations. However, the power stored in the batteries is not unlimited, and therefore mobile power banks or portable power supplies which can store more power appear in the market. The user may carry a mobile power bank or portable power supply. When power in the batteries of the mobile device is used up, the mobile device can be connected to the mobile power bank or portable power supply to receive real-time power supply.
In general, a portable power supply should have both charging and discharging functions. Conventionally, the charging and discharging functions are realized on different terminals; that is, the portable power supply may include a power input terminal and a power output terminal, for performing charging and discharging functions, respectively. However, the design of portable electronic devices becomes lighter and smaller, and thus the shell size may also become smaller, such that the number of pins or connection ports which can be deployed on the shell becomes fewer accordingly. Therefore, the new type portable power supplies are required to integrate the power input function and power output function on the same terminal to further achieve reduction of the size. In such a condition, the portable power supplies should possess satisfactory detection performance, in order to accurately determine whether it should be operated in the charging mode or discharging mode.
In the prior art, determination of the charging mode and discharging mode are realized by voltage detection. When an external voltage received by the portable power supply is greater than a specific threshold value, the portable power supply will determine that an external power source exists and thereby switch to the charging mode to receive power. When the external voltage is smaller than the threshold value, the portable power supply will switch to the discharging mode. However, the detected external voltage may be influenced due to various factors such as the impedance in the power supply path or magnitudes of currents drawn from the power source; hence, the voltage may possess irregular fluctuations, which result in wrong determination of the system. Thus, the portable power supply may switch to a wrong operation mode. For example, when the current drawn by the batteries of the portable power supply exceeds a predefined upper limit of the external power source, the input voltage may significantly fall. At this moment, the portable power supply may determine that the external power source does not exist and thereby stop charging or switch to the discharging mode, which results in instability of charging and also reduces the charging efficiency. Thus, there is a need to provide another power supply system, in order to realize more accurate power detection.